Occupant restraint systems and, in particular, inflatable occupant restraint systems, are increasingly being used in automotive vehicles. Nearly every vehicle now produced has driver and passenger front airbags. Side airbags are also increasingly being used in automotive vehicles. Side airbags use lateral acceleration sensors to detect the lateral acceleration of the vehicle and thus the presence of a side impact. In response to lateral acceleration, the side airbags are deployed.
Another newer type of inflatable occupant restraint system is a side curtain airbag. The side curtain airbag deploys from the ceiling or near the roof header and extends downward in front of the side windows of the vehicle. This system is designed to protect occupants in rollover conditions.
Another type of non-inflatable system is a pretensioner system coupled to the seat belt. A pretensioner system reduces the amount of play in the seat belts upon a sensed condition.
Each of the above systems may potentially be employed during rollover of a vehicle. Commonly, an energy-based model is used to determine when rollover occurs. Therefore, an accurate determination of rollover is desirable for use in determining when to deploy the restraints.